build(deps): bump cython from 0.29.26 to 0.29.28 (pydantic#3871)

Bumps [cython](https://github.com/cython/cython) from 0.29.26 to 0.29.28.
- [Release notes](https://github.com/cython/cython/releases)
- [Changelog](https://github.com/cython/cython/blob/master/CHANGES.rst)
- [Commits](cython/cython@0.29.26...0.29.28)

---
updated-dependencies:
- dependency-name: cython
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -1,6 +1,6 @@
 # requirements for compilation and from setup.py so dependabot prompts us to test with latest version of these packages
 
-Cython==0.29.26;sys_platform!='win32'
+Cython==0.29.28;sys_platform!='win32'
 devtools==0.8.0
 email-validator==1.1.3
 dataclasses==0.6; python_version < '3.7'